Process for oxidizing mercaptans to disulfides in the presence of solid catalytic masses

ABSTRACT

A PROCESS FRO CONVERTING SULFUR COMPOUNDS IN PETROLEUM CUTS TO DISULFIDES COMPRISES CONTACTING THE PETROLEUM CUT WITH MOLECULAR OXYGEN AND WITH A SOLID CATALYTIC MASS INSOLUBLE INTHE LIQUID PETROLEUM CUT AND CONSISTING ESSENTIALLY OF AT LEAST ONE SOLID PHTHALOCYANINE OF A TRANSITION METAL, A SOLID CARRIER AND A SOLID ALKALI METAL OXIDE OR HYDROXIDE, THE AMOUNT OF THE TRANSITION METAL PHTHALOCYANINE BEING BETWEEN 0.05% AND 50% BY WEIGHT WITH RESPECT TO THE CARRIER WEIGHT AND THE AMOUNT OF THE ALKALINE METAL OXIDE OR HYDROXIDE BEING BETWEEN 10% AND 50% BY WEIGHT WITH RESPECT TO THE TOTAL WEIGHT OF THE CATALYTIC MASS. BY THE PROCESS, THE HERETOFOR CONVENTIONAL PRETREATMENT STEP OF MIXING THE PETROLEUM CUT WITH AN ALKALINE AQUEOUS PHASE IS NO LONGER NECESSARY.

United States Patent US. Cl. 208-206 9 Claims ABSTRACT OF THE DISCLOSURE A process for converting sulfur compounds in petroleum cuts to disulfides comprises contacting the petroleum cut with molecular oxygen and with a solid catalytic mass insoluble in the liquid petroleum cut and consisting essentially of at least one solid phthalocyanine of a transition metal, a solid carrier and a solid alkali metal oxide or hydroxide, the amount of the transition metal phthalocyanine being between 0.05% and 50% by Weight with respect to the carrier weight and the amount of the alkaline metal oxide or hydroxide being between 10% and 50% by weight with respect to the total weight of the catalytic mass. By the process, the heretofore conventional pretreatment step of mixing the petroleum cut with an alkaline aqueous phase is no longer necessary.

This invention has for object the oxidation of sulfur compounds and particularly mercaptans in the presence of solid catalytic masses.

It is known that the mercaptans contained in gasoline, kerosene, gas oils, naphthas and generally in the relatively light products from crude oil distillation or from petroleum refining are noxious particularly in view of their odor, their acidity and their corrosive properties.

Accordingly, all of these products must be refined before being sold on the market. This refining includes mercaptan removal, also called sweetening. In some cases the treatment is carried out in two stages: extraction of the mercaptans followed with an oxidation, or oxidation of the mercaptans followed with an extraction of the disulfides.

In other cases it is suificient to perform a sweetening of the gasoline, i.e. an oxidation of the mercaptans contained therein without removal of the sulfur products resulting from the mercaptan conversion, said products mainly consisting of disulfides, which are far less noxious than the mercaptans.

The present invention relates to a process for facilitating the direct oxidation of the mercaptans or salts thereof to disulfides, whereby there can be achieved the sweetening of solvents or of petroleum feedstocks.

The oxidation of mercaptans to disulfides is generally carried out in the presence of an aqueous solution of alkali (sodium hydroxide or potash), by means of gaseous oxygen or, more generally, air, in the presence of a catalyst.

The catalysts which were previously recommended are sulfonated derivatives of phthalocyanines of transition metals, particularly of cobalt and vanadium.

These derivatives may be deposited on carriers such as alumina, bauxite or coal, the latter being the most frequently used.

In some cases it is possible to deposit the phthalocyanine of the metal itself instead of a sulfonated derivative thereof, on the coal. The so-obtained catalyst is 3,686,694 Patented Aug. 22, 1972 then completely insoluble in the feedstock subjected to the sweetening treatment and in the alkaline phase.

Finally it has been recently shown that, instead of depositing the powders of the transition metal phthalocyanines on a carrier, it is sufficient to intimately mix such powders of the transition metal phthalocyanines with a carrier of high specific surface and particularly active carbon for obtaining very active catalysts. These mixtures are used under conventional sweetening conditions, i.e. oxidation by air in the presence of an aqueous solution of alkali.

Now, it has been discovered, according to a feature of this invention, that oxidation of mercaptans to disulfides may be carried out by means of oxygen, in the presence of a catalyst but in the absence of an alkaline aqueous solution.

To operate in the absence of an alkaline aqueous phase offers an actual advantage with respect to the conventional processes since the mixing steps can be omitted as well as the step of separating the two immiscible liquid phases, which, up to now, required the use of a decantation vessel.

The absence of the alkaline aqueous solution is made possible in view of the particular composition of the catalyst according to the present invention.

The process according to this invention for oxidizing sulfur compounds and more particularly mercaptans contained in the petroleum cuts or issued therefrom is char acterized in that said sulfurized products are contacted in the liquid phase with (a) a gas containing or able to supply molecular oxygen and (b) a solid catalytic mass prepared by admixing at least one solid phthalocyanine of a transition metal with a carrier having a specific surface between 50 and '500 mF/g. and with an alkali metal oxide or hydroxide, the amount of transition metal phthalocyanine being in the range of 0.05% to 50% by weight with respect to the carrier, the amount of alkali metal oxide or hydroxide being between 10' and 50% by weight with respect to the total weight of the catalytic mass. 1'

The carrier may be for instance coal (active carbon, animal charcoal, carbon black, coke, ordinary coal as such or treated, or any other coal obtained by the known methods or manufacture), alumina or silica. Preferably coal is used.

The transition metal contained in the phthalocyanine compound is preferably selected from cobalt, vanadium, copper, iron and/or nickel. The phthalocyanines used may be prepared by any one of the conventional methods. The phthalocyanines available on the market are generally suitable.

The alkali metal is generally potassium or sodium.

The mixture of the components of the catalytic mass may be prepared in different ways.

One way consists of admixing the carrier (coal for instance) and the phthalocyanine, thereafter impregnating said mixture, under dry condition with a solution of alkali metal hydroxide. There is thus obtained a paste which can be shaped in usual manner: for example by extrusion, compression or pellet forming. The shaped product is then dried in an oven at a convenient temperature, in most cases between 40 and C.

Another way comprises impregnating the carrier, under dry condition, with the solution of alkali metal hydroxide, drying it and then admixing it with phthalocyanine. The shaping step is then more difficult to carry out and it may be advantageous to add a binding agent such as graphite, bentonite, magnesia or calcium oxide. It is also possible to admix three components: phthalocyanine, carrier and alkali metal oxide or hydroxide. This mixture may be 3 directly formed in pellets or, with the use of a binding agent, shaped into extrudates, balls or pills.

The proportions of transition metal phthalocyanine and carrier used to form the catalytic mass may be varied. Very small amounts of phthalocyanine may be used but, in order to obtain a good homogenization of the mixture it is advantageous to use it in a proportion of at least 0.05% by weight with respect to coal.

The catalytic mass of this invention is preferably used in the wet state. Its water content will depend on the operating conditions and on the feedstock subjected to oxidation. Good results have been obtained with proportions between 1 and 40% and preferably between 5 and 25% by weight of water with respect to the total catalytic mass.

The so-defined catalytic mass provides for the direct oxidation, by means of molecular oxygen, air or any other oxygen-containing or supplying gas, such as a nitrogen oxide, hydrogen peroxide or any other peroxide, of mercaptans or salts thereof to disulfides, and, contrarily to the usual catalysts, said catalytic mass makes possible the operation in the absence of aqueous phase.

The mercaptans to be oxidized according to the process of this invention are those contained in various media, particularly in solvents or petroleum products such as gasolines, kerosenes, gas-oils, naphthas and the like. The mercaptans oxidized according to the process of the invention may be either of the alkyl or cycloalkyl type or of the aryl type and contain for example up to 30 carbon atoms in their molecule.

The catalyst may be used in any usual manner: for instance in a moving bed, a fixed bed or according to a percolation method. It can also be used inside the storage tank for the feedstock which has to be subjected to the sweetening treatment. It is often preferable to make use of a percolation system.

According to the mercaptans content and the composition of the feedstock subjected to the sweetening treatment, here can be used oxygetn in a dissolved state or an oxygen-containing gas which is bubbled therethrough.

The reaction is conducted at a temperature generally in the range of to 70 C., preferably between and C.

The catalyst used according to the present invention is completely insoluble in and does not change the color or the stability to color of petroleum feedstocks. It is in some cases recommended to add to the reaction medium small amounts of alcohol or ketone which may significantly favor the reaction.

Although the catalyst used according to this invention is very active at the ambient temperature for oxidizing diflficultly oxidizable mercaptans such as thiophenol, there can be introduced in the catalyst, without inconvenience, small amounts of sulfites or other salts, or still other mercury, manganese and copper compounds known as activating agents in the oxidation of mercaptans to disulfides. The catalyst according to the invention provides for the sweetening of large amounts of petroleum feedstocks before losing its activity. It is easily regenerated, for instance by washing with a mixture of alcohol and acetone.

The following non-limitative examples are given for illustrative purposes.

EXAMPLE 1 This example relates to the manufacture of a catalyst containing 13% by weight of cobalt phthalocyanine, 36% of coal and 45% of potash. 19 g. of cobalt phthalocyanine are admixed with 57 g. of coal. The resulting mixture is impregnated with 100 cc. of a saturated potash solution. The so-obtained paste is extruded and dried for 4 hours at 50 C.

EXAMPLE 2 The catalyst of Example 1 has been used for oxidizing nbutyl mercaptan to disulfide.

There is used a percolator wherein are placed 5 g. of the catalyst having a volume of about 10 cc. The mercaptan containing liquid (350 cc. of toluene and 0.1 mole of n-butylmercaptan) is circulated therethrough at a rate of 1 liter per hour and is recycled. Air is simultaneously injected at atmospheric pressure through a fritted glass, at a rate of 4 liters per hour. The catalyst is maintained at 23 C. by means of a jacket for thermal regulation by a fluid circulating therein.

Two runs of the feedstock have been suflicient to obtain a negative doctor test (Standard NF MO 7-029).

EXAMPLE 3 The catalyst of Example 1 has been used for sweetening a highly aromatic straight-run gasoline having an initial boiling point of C. and containing 500 p.p.m. of sulfur in the form of mercaptans.

Under the conditions stated in Example 2, this feedstock has been sweetened after 3 runs. It no longer had a nauseous odor and its doctor test was negative.

EXAMPLE 4 A catalyst has been prepared by admixing 24 g. of activated vegetal coal with 0.024 g. of cobalt phthalocyanine. This mixture has been impregnated with 23 cc. of a saturated potash solution and has been extruded and dried for 3 hours at 60 C.

EXAMPLE 5 The catalyst of Example 4 has been used for sweetening a feedstock consisting of toluene containing 465 p.p.m. of sulfur in the form of n-butyl mercaptan and 47 p.p.m. of sulfur in the form of t-butyl mercaptan.

Over 15 g. of said catalyst, maintained at 23 C., was passed a mixture of air with the feedstock. The How rate 0 of air was maintained at 4 liters/hour and the flow rate of the feedstock was that corresponding to a passage velocity of 30 cc. of liquid per cc. of catalyst and per hour: VVH=30. The feedstock collected at the outlet was completely sweetened (negative Doctor test).

EXAMPLE 6 A catalyst has been prepared by impregnating 30 g. of activated vegetal coal with 30 cc. of a 70% potash aqueous solution. The resulting paste has been mixed with 0.15 g. of cobalt phthalocyanine and then extruded and dried for 3 hours at 60 C.

EXAMPLE 7 The catalyst of Example 6 has been used in the experimental conditions of Example 5. The feedstock of Example 5 further contained 45 p.p.m. of sulfur in the form of thiophenol. After passage through the percolator at a VVH of 50, the feedstock was issuing in a completely sweetened state. 15 liters of this feedstock were so sweetened without any loss of activity of the catalyst.

EXAMPLE 8 A catalyst has been prepared by admixing 25 g. of active carbon with 0.025 g. of cobalt phthaloeyanine. The resulting mixture after impregnation with 23 cc. of a saturated sodium hydroxide solution, has been extruded and dried for 3 hours at 60 C.

EXAMPLE 9 The catalyst of Example 8 has been used for sweetening the same feedstock as in Example 5 and under the same operating conditions. The feedstock outflow was completely sweetened (negative Doctor test).

EXAMPLE 10 A catalyst has been prepared by impregnating 30 g. of activated vegetal coal with 30 cc. of a 70% potash aqueous solution. The resulting paste has been mixed with 0.15 g. of copper phthalocyanine and then extruded and dried for 3 hours at 60 C.

EXAMPLE 11 The catalyst of Example has been used for sweetening the same feedstock as in Example 5 under the same operating conditions as in Example 5. The feedstock recovered at the outlet was completely sweetened (negative Doctor test).

What we claim as our invention is:

1. A process for oxidizing mercaptans or salts thereof to disulfides, said process comprising contacting said mercaptans or salts thereof contained in a petroleum cut liquid with molecular oxygen and with a solid catalytic mass insoluble in said liquid petroleum cut and consisting essentially of at least one solid phthalocyanine of a transition metal a solid carrier and a solid alkali metal oxide or hydroxide, the amount of the transition metal phthalocyanine being between 0.05% and 50% by weight with respect to the carrier weight and the amount of the alkaline metal oxide or hydroxide being between 10% and 50% by weight with respect to the total weight of the catalytic mass, said process being conducted in the absence of a pretreatment step of mixing said petroleum cut with an alkaline aqueous phase.

2. A process according to claim 1, wherein the metal contained in the phthalocyanine composition is selected from the group consisting of cobalt, vanadium, copper, iron and nickel.

3. A process according to claim 1, wherein the carrier is coal.

4. A process according to claim 1, wherein the alkaline metal is selected from potassium and sodium.

5. A process according to claim 1, wherein the catalytic mass further contains from 5 to by weight of water.

6. A process according to claim 1 wherein there is added to the catalytic mass a binding agent selected from graphite, bentonite, calcium oxide and magnesia.

7. A process as defined by claim 1 wherein said molecular oxygen is in the form of air.

8. A process as defined by claim 1, said liquid media being a petroleum cut, said process being conducted in the absence of a subsequent step of decanting said petro leurn cut from said alkaline aqueous phase.

9. A process as defined by claim 1, said liquid media having added thereto a ketone or alcohol.

References Cited UNITED STATES PATENTS 3,471,254 10/1969 Urban 252-431 N X 3,108,081 10/1963 Gleim et al. 252-431 N X 2,976,229 3/1961 Brown et a1. 208-207 X JOSEPH REBOLD, Primary Examiner D. R. PHILLIPS, Assistant Examiner US. Cl. X.R. 

